ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

5pUW14. Time-domain propagation of signals in a strongly refractive shallow-water waveguide and the extraction of ocean properties.

N. A. Sidorovskaia

Dept. of Phys., Univ. of New Orleans, New Orleans, LA

A. I. Khil

Russian Academy of Science, Nizshy Novgorod 603600, Russia

M. F. Werby

Naval Res. Lab., Stennis Space Center, MS

The complex pressure from a point source is calculated over the frequency range between 1 and 5 kHz in steps of 0.2 Hz as a function of depth and range for a strongly ducted shallow-water waveguide. The waveguide is composed of an 80-m water column over a fluid half-space defined by a compressional velocity of 1650 m/s and a density of 1.6 relative to water. Attenuation in the bottom is 0.25 dB/(lambda). The velocity in the water column varies from 1540 at the surface to 1513 m/s at the bottom where a pronounced gradient exists between 30 and 60 m, with the remaining regions being weakly dependent on depth. A series of time-domain calculations are carried out from the stored frequency data for pulses in terms of (1) pulse widths, (2) central frequency, (3) depth of detection, and (4) range of detection. The central notion is that the pulse amplitude is strongly correlated with depth due to ducting effects. Further, pulse widths and the principle arrival time adds more information on ocean properties such as the velocity profile and some aspect of seafloor geoacoustic characteristics. Unambiguous systematics that suggest a tool useful for extraction of ocean data are reported. [Work sponsored by ONR.]